1. Technical Field of the Invention
The present invention relates to a lag correction technology of audio samples in which sample mismatching between nodes in a ring audio network system is corrected based on the positional relationship of the nodes.
The present invention also relates to a technology for a ring audio network system in which transmission delay times in the system are taken into consideration and the output times of audio signals from nodes are corrected, thereby correcting the phase difference of all the nodes in the system.
2. Description of the Related Art
Conventional technologies for audio signal communication in an audio network system used for PA such as plays and concerts, music production, and private broadcasting include CobraNet™ described in Non-Patent Reference 1, SuperMAC (registered trademark) described in Non-Patent Reference 2, and EtherSound (registered trademark) described in Non-Patent Reference 3. Any of them is a technology for transmitting audio signals over the Ethernet.
Conventional technologies used in a telephone line network include a ring communication network such as FDDI/TokenRing. In this scheme, a token (i.e., the right to transmit data) circulates through nodes connected in a ring so that only a node which obtains the token is permitted to transmit data.
One can consider an audio signal (audio sample data) transmission scheme using the conventional ring communication network. FIG. 13 illustrates an example of a ring audio network system. A signal circulates through nodes reciprocally along the nodes in the order of node 1301node 1302node 1303node 1302node 1301. FIG. 14 illustrates another example of the same ring audio network system. In this example, nodes 1401 to 1406 are physically connected in a ring in the named order. A packet transmitted from the master node 1401 circulates once in one sampling cycle (or time) in the order of 140114021403140414051406. A storage region of audio sample data of a plurality of channels (Ch) is allocated in the packet and each node transmits data by loading it into a storage region of a suitable channel in the packet.
However, in the system in which data is transmitted in a ring as described above, sample data of the same sampling cycle in which corresponding sample data is stored in the circulated packet by the node 1404 is extracted from the node 1406, while sample data of a different sampling cycle is extracted from the node 1403. This is because, when the sample data stored in the node 1404 reaches the master node 1401, the sample data is incorporated into a packet that circulates in the next sampling cycle, and the node 1403 then receives the packet. By such a manner, there is caused sample time mismatching between nodes in a conventional ring audio network system. Usually, such sample mismatching causes almost no problem. However, a variety of professional audio devices may not permit such sample mismatching.
Further in the conventional system in which data is transmitted in a ring as described above, it is difficult to accurately match output timings of audio signals of all nodes of the system. Particularly, as long as the system uses transmission lines, the system suffers from delay in signal transmission through the transmission lines. Processing in each node also causes a delay. Usually, such a small delay causes almost no problem. However, a variety of professional audio devices may not permit even such a small time delay, and there may be a desire to eliminate even the phase difference of audio signals output from all nodes. For example, in order to strictly design and set up a line array speaker system, it may be necessary to take into consideration even such a small delay.